The present invention relates to a precision device for attaching removable dental prothesis specially designed for the upper and lower dental arch free ends. The device is responsible for interlocking the removable prosthetic portion to a support tooth.
A prothesis with a device of this kind is disclosed in the Brazilian Patent document PI 199961 which provides a male fitting member and a female fitting member of a cylindrical cross-sections, the former being implanted in the natural tooth adjacent to a dental arch defect which is intended to be filled and the latter member being fastened to a lateral face in the movable prosthetic portion. The movable portion is vertically inserted, so that the female member fits on the male member. There is also provided in each member a vertical slot that allows pressure adjustments when both members are fitted together.
The Brazilian Patent document PI 7704662 describes a dental prothesis which can substitute for the movable bridge's clamp. The apparatus is also composed of a male member and a female member of a rectangular cross-sections, vertically fitting together.
An alternative construction for the above mentioned prothesis is provided in another Brazilian Document PI 8606582, which describes an apparatus comprising the preparation of one or more support crowns associated with the male member of a locking system, which consists of a fitting box provided with a hole having a narrower opening in its upper portion. The other portion of the apparatus is removable, consisting of a double bar metal base. The base is associated with the female member of a locking system. The female member is provided with a lock pin, where it is adapted to a receiving hole in the male member.
Other fittings of this kind are known through U.S. Pat. No. 4,634,380 and 4,768,957, German 3,419,144 and Swiss 649,209, which are primarily fittings consisting of male and female members of various shapes, being provided with a lock pin. When these fittings are used for attaching a removable portion in the dental arch free ends to a support tooth, they need stabilizer metal bars, which cross-over the palate or the mouth's lingual portion, from side to side.
U.S. Pat. No. 4,698,020, Swiss 579,387 and 644,483 and French 7,922,160 refer to fittings with similar features to the above mentioned, but have differences as to the attachment of the removable portion to a fixed portion. The kind of attachment used in these fittings is made by pressure during fastening, which is caused by a spring whose only purpose is to provide a more precise and secure attachment.
All existing removable precision prosthetic apparatuses, when used on free ends, present serious clinical and aesthetic problems such as loss of mucous membrane sensitivity, gingivitis, annoyance during adaptation, causing marks on the mucous membrane, acidity, and other problems, due to the devices used in the apparatus for attaching a removable prosthetic portion to a fixed prosthetic portion.
Besides the above mentioned drawbacks, it should be noted that these devices have no retention features of their own from the apparatus' movable portion to the fixed portion thereof and none for distributing and balancing the side forces occurring during mastication. Thus, stabilizing bars are needed in order to compensate such problems and to provide a greater strength to the apparatus as well.
In an attempt to solve these problems, Brazilian Patent Document PI 8606582 uses an elastic connection system developed to join a saddle to the other components of a partial removable prothesis, through non-rigid mechanisms that allow some freedom of controlled and independent movements for the connecting element.
This kind of non-rigid mechanism, made of metal bars having a greater coefficient of elasticity than the support elements and the periodontal ligament fibers of pilar teeth, allows the side forces imposed on the very support teeth to be minimized.
However, these elastic bars cannot effectively solve the masticatory force distribution on the mucous membrane. Most of the force concentration is shown to fall directly on the retention teeth, which causes an unfitting mastication movement, technically called deocclusion, and teeth mobility, causing headaches, ear pain and lacrimation in the patent. Such effects and the very own bar cause several of the above mentioned clinical and aesthetic problems.
Regarding the elastic property provided to such bars, its action is not effective, since its effect is impaired by their anatomical configuration, having a flat and inclined shape, in accordance with the osseous slope anatomy of the mandible lingual face's mucous membrane, therefore not allowing the elastic action to absorb the masticatory force.